Sound recording apparatus



Oct. 26, 1937. E. w. KELLOGG SO UND RECORDING APPARATUS Filed Jan. 5, 1935 INVENTOR fan M0 n1 I121 066 ATTORNEY Patented Oct. 26, 1937 PATET OFFICE SOUND RECORDING APPARATUS Edward W. Kellogg, Moorestown, N. J., assignor to Radio Corporation of America, a corporation of Delaware Application January 5, 1935, Serial No. '531 3 Claims.

This invention relates to improvements in sound recording apparatus, and more particularly in the variety thereof which is used in re-recording from an original sound record to a duplicate sound record adapted either for the production of prints or for direct sound reproduction.

-One object of the invention is to provide a method and apparatus for producing what is known as an anti-ground-noise sound record from an ordinary sound record.

Another object of the invention is to provide a method and apparatus for producing such an anti-ground-noise record which is capable of direct sound reproduction.

Another object of the invention is to provide such a method and apparatus as will permit the use of a. properly designed amplifier including appropriate time lag in the operation thereof to prevent oscillation or response to audio-frequency impulses in the operation of the antiground-noise shutter, in combination with a reproducing system for the operation thereof from an original sound record which will cause the shutter to be operated at the same time as the sound being recorded.

Another object of the invention is the provision of a new type of galvanometer which will simultaneously record sound waves and provide the blackened anti-ground-noise area on the sound track.

The invention is particularly adapted to use with sound records of the variable area type.

My invention involves an improvement upon the method and apparatus shown and described in Greentree Patent 1,971,181 and McDowell Patent 1,855,197, and provides for the re-recording of sound from a photographic record to another photographic record, thereby permitting such modification of the characteristics of the record as may be desirable in theelectrical amplifying circuits used in the re-recording, and further involves the application of ground noise elimination to such re-recording apparatus and method. 45 In the preferred form of the invention, I provide a particularly novel and convenient re-recording galvanometer having two mirrors similarly cooperative with the optical system for simultaneously but independently recording the sound 50 waves, and a record corresponding to the envelope of the sound waves for the purposes of eliminating ground noise.

In the drawing: Fig. 1 shows diagrammatically a re-recording 55 apparatus for producing a negative sound record or the anti-ground noise type adapted for the production of positive prints.

Fig. 2 shows the double galvanometer for the production of a positive anti-ground noise sound record directly. 5

Referring first to the system shown in Fig. 1,

l indicates a sound record which is preferably a positive sound record of the variable area type, and which is moved downwardly past the gate member 2 which may be a curved plate or ro- 10 tating drum or any of the usual types of sound gates provided it is adapted to sound take-off at two points separated by a short distance measured in the direction of travel;

The sound reproducing optical system con- 15 sists of the usual type of exciter lamp 3, the condenser lens 4, the slit 5 and the objective lens 6 forming an image 1 of the slit 5 upon the film.

From this image 1, the light diverges to the photocell 8. 20

The current passing through the photocell 8 is amplified by an audio frequency amplifier 9 of any customary or usual type, and is then passed to the galvanometer In which is likewise of any type adapted to such sound recording. 25 This galvanometer l0 includes a movable mirror II uponwhich light is directed from the lamp l2 by the lens l3. Lens l4 causes an image of the aperture IE to be formed in the plane of the slit 16. The position of this image is de- 30 termined by the angle which the mirror I I makes with the incident light. Therefore, rotational vibrations of the mirror cause movements of the image. Light enters the lens I8 from only that portion of the slit [6 which is illuminated, or 35 covered by the image of the aperture I5. Thus the movements of the mirror result in varying fractions of the slit It being illuminated, and the length of the line of light imaged on the film also varies in response to movements of the mirror. The film I9 is a. photographically sensitive film of any type appropriate for the production of a sound record.

Before any given point of the soundtrack of the film l reaches. the point 1, it passes the point 1' separated a predetermined distance from the point 7, as will be more particularly described later, and at this point there is another photoelectric take-oif consisting of exciter lamp 3', lens i, slit 5', lens 6', and photocell 8', all of which operate in the same. manner as the corresponding elements of the sound take-off first described.

From the photocell 8' current passes through the amplifier 20 and then through the rectifying amplifier 2|, these two elements being'preferably constructed in thefmanner shown and described in the article by Barton Kreuzer in the Journal 7 .of The Society of MotionPicture Engineers? for June, 1931, pagesflfi'llto 683, this issue of the said journal being volume 16, No. 6. r

The output from the amplifier 2I goes to the galvanometer 22 which carries a shutter 23 adapted to cover up a portion of the slit 5 cor responding to the unused portion' of the soundtrack upon the film I. When the modulation is very slight, the shutter will move closer to the center and prevent the transmission of light through the transparent portion of theso'und-r track above the peaks of the'images ofthe sound waves, while if the modulation is increased, the shutter will unmask a correspondingly larger portion of the slit 5 in order to permit light to pass 'through-therentire images of the 'soundwaves.

The output from the amplifier 2| also. passes through a galvanometerifl'Which'is similarin' construction and operation to' the fgalvanometer r '22 and serves to mask ofi a corresponding portion of the light passed to the sound record strip'l9 7 so that the portion of the soundrecord im-;

' pressed upon the member [9; which'would otherwise be black but unmodulated; is rendered clear andtherefore a print therefrom upon a'positive film will'have, in addition to the black print'of the sound record} a blackened portion corresponding to the portion of the sound record I which has been masked by the member 23.

'' 'It will be apparent that the effect of the member 23 :will be toiprev'ent the reproductionjof bers, necessarily, introduce a certain'amount of] lgroundvnoise from the clear or unmodulated portion of the soundtrack on the film I, thereby preventing the recording of such ground noise upon the film I9, and "at the same time the operation of the mask 25, inpr'oviding a correspondingly clear portion upon the film 19, will correspondingly prevent any ground noise frorn'the film it self in the reproduction of prints made from r I the film l9;

The amplifier and amplifying rectifiers 20 and 2|, plus the necessity ofovercoming the inertia of. the masks 23, 25 and their supporting memtime-lag between'the photocell 8 and the movements of the galvanometers 22 and 24, and the optical system 3'$ is accordingly; spaced from the optical'system 3-6 'a'distancesuch that the time of travel of the film'from the point I to the point 1 corresponds to this-time lag and, therefore, the position of the masks 23 and 25 the sound record being thenreproduced through the photocell 8 and amplifier 9.

Referring now to the'construction shown in Fig. 2': It is some times desirable to record 'directly or to produce by a re-recording process, as described above, a sound record adapted to direct reproduction without making prints therefrorn, and the apparatus shown in this figure is intended forthe production of such sound recsoundtrack of the film I9.

eludes an optical system similar to' that shown in,

ords with the'portion of the soundtrack blackened I to correspond to the clear portion provided on the This apparatus inthe recording'apparatus of Fig. 1, and including the slit 'lfifthelens l1, andthe lens l8 which serve to directthe light from themirror H in the manner already'described.

For the .galvanometer, l0 and mirror ll,'there is substituted, howeverfa double galvanometer consisting'of a movable coil 10 and a mirror will at all times correspond to the amplitude of I l'ior recording the sound in the same'mani Co-axial with this mirror II, or substantially so, is a mirror nerv as the coil l8 and mirror II.

21 which serves to direct light from'the same source, upon the slit I6, the limits of the light beam being defined by the same mask 15. This mirror The operated-bythe coil 28 which mo'ves between thepolepieces29 of a magnet, the coil 28 being fed with current from the amplifier 2| in the same manner as the coil 24 shown" in Fig. 1. It will be apparent that movement of the mirror 2'! instead of producing a clear portion on the sound record 26 will produce a blackenedpor j-tion, and by properly adjusting the'position of;

the mirror, this blackened portion can be made to correspond to the clear portion produced on the film I9 so that'the sound record produced upon the photographically sensitive film 26 can,

after development, etc. be played directly in an appropriate sound reproducer, and with a reductionof. ground noisecorresponding'to the reduced width of clear film, exactly as was the case with a positive print from the film l9. 7

. It will be apparent that the double galvanome ter of Fig; Z'is not limited to usein a i e-recording apparatus as shown in Fig. 1, butthat it can also 7 be used in making original sound records for direct'reproduction. It is also obvious that other electro-mechanical devices than the moving coils 22, 24,28, or the magnetic armature devioes'lu,

l0, may be employed 'to'actuatejthe vanes23,

25, or the mirror 21, orthe mirrors l I, ,I l'.

Having described my invention, I claim: I '1. Sound re-reco rding'apparatus for producing a film sound record 'without'ground noise,

from a variable area film 'sound record having a substantially constant average light transmission, comprising meansrfor passing a beam o'f light through said sound record,rphotoele'ctric mea'nsfor receiving said light after it is passed through said record, :means connected" to said photoelectric means for producing a current corresponding to the envelope of the sound waves,

means for directing a second beam of light through said sound record, photoelectricmeans for reproducing sound'from the light transmitted through the film from said second means, means for directing a third beam of light onto unexposed film, means connected to said sound remodulating the said third I producing means ,for beam of' light in accordance with sound vibrations, means in the path ofthe second said beam of light actuated by the current corresponding to the said envelope of the sound waves for obscuring the clear portion of the said sound record in accordance with the envelope of the sound Waves to be reproduced, and means in the said sound recording optical system connected to the 7 said envelope current producing means, for shading the portion of the sound record which is being producedin accordance with the sound impulses.

2. Sound re-recording apparatus forproduc ing a film sound record without ground noise,

from a variable area film sound record having a substantially constant average light transmis- W 'sion, comprising means for passingrafbea'm of light through said sound record, photoelectric means for receiving said light after it is passed {through said record, means connected to said photoelectric means for. producing a currentcorresponding to the envelope of the soundwaves, means for directing a second beam of light through said sound record, photoelectric means for reproducing sound from the light transmitted through the film from'said second means, means for directing a third beam of light onto unexposed film, means connected to said sound reproducing means for modulating the said third beam of light in accordance with sound vibrations, means in the path of the second said beam of light actuated by the current corresponding to the said envelope of the sound waves for obscuring the clear portion of the said sound record in accordance with the envelope of the sound waves to be reproduced, and means in the said sound recording optical system connected to the said obscuring means and the said envelope current producing means, for shading the portion of the sound record which is being produced in accordance with the sound impulses.

3. Sound re-recording apparatus for producing a film sound record without ground noise, from a variable area film sound record having a substantially constant average light transmission, comprising means for passing a beam of light through said sound record, photoelectric means for receiving said light after it is passed through said record, means connected to said photoelectric means for producing a current corresponding to the envelope of the sound waves, means for directing a second beam of light through said sound record, photoelectric means for reproducing sound from the light transmitted through the film from said second means, means for directing a third beam of light onto unexposed film, means connected to said sound reproducing means for modulating the said third beam of light in accordance with sound vibrations, means in the path of the second said beam of light actuated by the current corresponding to the said envelope of the sound waves for obscuring the clear portion of the said sound record in accordance with the envelope of the sound waves. to be reproduced, and means in the said sound recording optical system connected to the said envelope current producing means, for shading the portion of the sound record which is being produced in accordance with the sound impulses, the said two means for passing beams of light through the sound record being spaced longitudinally of the record by a distance corresponding to the time of the delay in the said envelope currentproducing means.

EDWARD W. KELLOGG. 

